In an ultrasound imaging system, an ultrasound transducer is composed of a group of transducer elements. An ultrasound imaging process is required to transmit an ultrasound wave and receive echoes of the ultrasound wave, and each of the transducer elements in the ultrasound imaging system is connected to a transmitter and a receiver. Generally, to save cost, multiple receivers will share one echo processing unit.
During imaging, each transmitter transmits a delayed ultrasound pulse via the transducer element into which it is connected. When each of the transducer elements in the ultrasound transducer transmits well-defined delayed ultrasound pulse respectively and simultaneously, the transmitted ultrasound pulse energy can be focused in the desired position and direction. These transmitted ultrasound pulses will be reflected by the detected tissue. The transmitted ultrasound pulse is received by the receiver. The time for various transducer elements to receive the ultrasound pulse even reflected from the same position varies from one to another. The echoes received by these different transducer elements are amplified, delayed and then summed to form a focused received beams.
A medical ultrasound system forms two-dimensional images by means of the received beams (or referred to as scan line), each being referred to as a frame of image. The total number of the frames of the images generated per second is referred to as the frame rate, which is an important parameter. A high frame rate is the basic condition for truly reproducing a fast moving tissue. The frame rate may be improved by reducing the scan density, but it is achieved at the expense of the image spatial resolution. Alternatively, a high frame rate may be obtained by means of multi-beam, which means that multiple receive lines are generated in a single transmission.
U.S. Pat. No. 5,469,851, entitled “Time Multiplexed Digital Ultrasound Beamformer”, discloses a digital ultrasound beamformer, which is capable of forming two or more beams simultaneously by means of time multiplexing. According to the technical solutions, the coefficient generator provides delayed data to the delay circuit multiplexed in each processing channel, and in the formation process, the apodization parameters of each channel are loaded with apodization parameter RAM. However, the invention concerned is not related to dynamic apodization, fast focus-changing imaging and fast frequency-changing imaging.